The reason this doesn’t work is because of UAC (User Account Control). By default Vista doesn’t allow UAC elevation over the network with a local user account.
There’s a registry key that we can use to change this behaviour.
Manual Registry Hack
Open regedit.exe then navigate down to the following key.
If it doesn’t exist add a new 32-bit DWORD value named LocalAccountTokenFilterPolicy and set the value to 1.
At this point you can map to the C$ share and also perform some other administrative tasks remotely.